In a statement, it said: “Their Royal Highnesses The Duke and Duchess of Sussex are very pleased to announce that The Duchess of Sussex is expecting a baby in the Spring of 2019.”

Their baby will not be a prince nor a princess, nor an HRH because George V limited titles within the Royal Family in 1917.

Instead, if the baby is a boy he wwould be known as Earl of Dumbarton – because a first son of a duke is allowed to use one of his father’s other lesser titles as a courtesy title.

Harry was also made the Earl of Dumbarton on the morning of his wedding, as well as being given a dukedom.

If the baby is a girl, she would be Lady (first name) Mountbatten-Windsor.

It is highly unlikely the child will ever be monarch, as they will have three cousins – Prince George, a future king, and Princess Charlotte and Prince Louis – who are further up the line of succession.

Their Royal Highnesses The Duke and Duchess of Sussex are very pleased to announce that The Duchess of Sussex is expecting a baby in the Spring of 2019. pic.twitter.com/Ut9C0RagLk

The baby will be a great-grandchild of the Queen and the Duke of Edinburgh, and the Prince of Wales’s grandchild and the Duke and Duchess of Cambridge’s niece or nephew.

The Duke and Duchess of Sussex attended the wedding of Princess Eugenie and Jack Brooksbank in Windsor last Friday (PictureL PA)

It is likely that the baby will be born at the private Lindo Wing in St Mary’s Hospital, Paddington, where the Duchess of Cambridge had her three children.

Harry was also born there in 1984. It is close to Kensington Palace and well practiced at dealing with royal births, and the publicity surrounding them.

Harry and Meghan could apply for their child to have dual US-UK citizenship. Meghan is planning to become a British citizen – but it is not known whether she will hold dual nationality, and at present is still a US citizen.

According to the American Embassy in the UK, a child born outside of the US and in wedlock to a US citizen parent and a non US citizen parent, may acquire US citizenship at birth if the US parent lived in America for five years – two of which were after the age of 14.